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Spinpoint M8U-Internal Product Manual REV 3.4
77
INSTALLATION
The vendor, product, device, manufacturer, product, and serialnumber fields of the standard device descriptor
are not included in this descriptor since that information is constant for a device for all supported speeds. The
version number for this descriptor must be at least 2.0 (0200H).
The host accesses this descriptor using the GetDescriptor() request. The descriptor type in the
GetDescriptor() request is set to device_qualifier (see Table 6-8). If a full-speed only device (with a device
descriptor version number equal to 0200H) receives a GetDescriptor() request for a device_qualifier, it must
respond with a request error. The host must not make a request for an other_speed_configuration descriptor
unless it first successfully retrieves the device_qualifier descriptor.
6.3.6.4.4 Configuration Descriptor
The configuration descriptor describes information about a specific device configuration. The descriptor
contains a bConfigurationValue field with a value that, when used as a parameter to the SetConfiguration()
request, causes the device to assume the described configuration.
The descriptor describes the number of interfaces provided by the configuration. Each interface may operate
independently. For example, an ISDN device might be configured with two interfaces, each providing 64Kb/s
bi-directional channels that have separate data sources or sinks on the host. Another configuration might present
the ISDN device as a single interface, bonding the two channels into one 128 Kb/s bi-directional channel.
When the host requests the configuration descriptor, all related interface and endpoint descriptors are
returned.
A USB device has one or more configuration descriptors. Each configuration has one or more interfaces and
each interface has zero or more endpoints. An endpoint is not shared among interfaces within a single
configuration unless the endpoint is used by alternate settings of the same interface. Endpoints may be shared
among interfaces that are part of different configurations without this restriction.
Once configured, devices may support limited adjustments to the configuration. If a particular interface has
alternate settings, an alternate may be selected after configuration. Table 6-13 shows the standard
configuration descriptor.
Table 6-13: Standard Configuration Descriptor